Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $164.82   11.679%   $184.0693   $184.07   $184.05   $184.10  
  Purchase #2 $143.71   4.560%   $150.2632   $150.26   $150.25   $150.30  
  Purchase #3 $155.52   9.376%   $170.1016   $170.10   $170.10   $170.10  
  Purchase #4 $207.88   5.287%   $218.8706   $218.87   $218.85   $218.90  
  Purchase #5 $226.66   5.312%   $238.7002   $238.70   $238.70   $238.70  
  Purchase #6 $5.49   12.193%   $6.1594   $6.16   $6.15   $6.20  
  Purchase #7 $114.85   10.627%   $127.0551   $127.06   $127.05   $127.10  
  7 purchase totals = $1,018.93       $1,095.2194   $1,095.22   $1,095.15   $1,095.40